Rust creepage test is the most frequently used qualification test to assess the corrosion resistance of candidate offshore atmospheric coatings. End users and coating manufacturers are using either the ISO 12944-9 or AMPP TM21612 test standard to measure the rust creepage of candidate coating systems in the lab. The lab test results are used by end users for the offshore coating selection. Lots of effort are spending on this lab test without a good understanding of the mechanism. It takes six months to run the ISO 12944-9 test and three months to run AMPP 21612 test. It is of great advantage to understand the rust creepage mechanism. The purpose of this work is to study the underfilm corrosion to shed light on the rust creepage mechanism. With a good understanding of the mechanism, the coating manufacturers may speed up the development of successful protective coating systems for the offshore coating industry.
The service life of current offshore platform coatings are normally less than 10 years. It is very expensive ($100/ft2) to rehabilitate the offshore platform coatings in the field. Therefore, facility owners are very anxious to select the long-life coatings. The candidate coatings are normally tested in the lab following the ISO(1) 12944-91 or the AMPP(2) TM216122 standard. The selection of offshore atmospheric coatings is based on the rust creepage test (ageing resistance), if the ISO test standard is used to test candidate coating systems. Rust creepage is one type of the underfilm corrosion with limited publications in the literature on the rust creepage mechanism. This is the purpose of this work to study the under film corrosion mechanism to shed light on the rust creepage mechanism. Hopefully, this paper can provide guidance to coating manufacturers in the development of long life offshore coating systems.
